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When using PSK for TLS authentication, look up and use the PSK ID requested by the client #379

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When using PSK for TLS authentication, look up and use the PSK ID requested by the client #379

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9b6608d
When using PSK for TLS authentication, look up and use the PSK ID req…
tkEmLogic Apr 20, 2026
b283e1d
Ensure that the size of the PSK ID requested by the client does not e…
tkEmLogic May 5, 2026
2cc5eea
Return NX_SECURE_TLS_INCORRECT_MESSAGE_LENGTH from _nx_secure_process…
tkEmLogic May 15, 2026
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21 changes: 18 additions & 3 deletions nx_secure/src/nx_secure_generate_premaster_secret.c
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Original file line number Diff line number Diff line change
Expand Up @@ -280,9 +280,24 @@ UINT pre_master_secret_size;
/* Now, using the identity as a key, find the PSK in our PSK store. */
if (session_type == NX_SECURE_TLS_SESSION_TYPE_SERVER)
{
/* Server just uses its PSK. */
psk_data = tls_credentials -> nx_secure_tls_psk_store[0].nx_secure_tls_psk_data;
psk_length = tls_credentials -> nx_secure_tls_psk_store[0].nx_secure_tls_psk_data_size;
/* Attempt to find the PSK ID requested by the client in the ClientKeyExchange message. */
psk_length = 0;
const UINT client_psk_id_size = tls_credentials -> nx_secure_tls_remote_psk_id_size;
const UCHAR* client_psk_id = tls_credentials -> nx_secure_tls_remote_psk_id;
for (i = 0; i < NX_SECURE_TLS_MAX_PSK_KEYS; i++)
{
if ((client_psk_id_size == tls_credentials -> nx_secure_tls_psk_store[i].nx_secure_tls_psk_id_size) &&
(NX_SECURE_MEMCMP(client_psk_id, tls_credentials -> nx_secure_tls_psk_store[i].nx_secure_tls_psk_id, client_psk_id_size) == 0))
{
psk_data = tls_credentials -> nx_secure_tls_psk_store[i].nx_secure_tls_psk_data;
psk_length = tls_credentials -> nx_secure_tls_psk_store[i].nx_secure_tls_psk_data_size;
break;
}
}
if (psk_length == 0)
{
return(NX_OPTION_ERROR);

@fdesbiens fdesbiens May 11, 2026

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You return NX_OPTION_ERROR when the requested PSK identity is not found. Existing PSK lookup helpers return NX_SECURE_TLS_NO_MATCHING_PSK, which maps to unknown_psk_identity. NX_OPTION_ERROR falls through to an internal-error alert. Use the TLS-specific error, and preferably scan only nx_secure_tls_psk_count or share
the existing lookup behavior.

@tkEmLogic tkEmLogic May 15, 2026

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Fixed, return code changed to NX_SECURE_TLS_NO_MATCHING_PSK.

}
}
else
{
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12 changes: 12 additions & 0 deletions nx_secure/src/nx_secure_process_client_key_exchange.c
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Expand Up @@ -178,6 +178,18 @@ UINT private_key_length;
/* Check for PSK ciphersuites and generate the pre-master-secret. */
if (ciphersuite -> nx_secure_tls_public_auth -> nx_crypto_algorithm == NX_CRYPTO_KEY_EXCHANGE_PSK)
{
/* Store the requested PSK ID in the TLS credentials. */
if (message_length < 2)
{
return NX_INVALID_PACKET;
}
tls_credentials -> nx_secure_tls_remote_psk_id_size = ((packet_buffer[0] << 8) | packet_buffer[1]);

@fdesbiens fdesbiens May 11, 2026

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It looks like you read past the handshake buffer for truncated PSK identities. The code checks message_length >= 2 and psk_id_size <= NX_SECURE_TLS_MAX_PSK_ID_SIZE, but never checks 2 + psk_id_size <= message_length before copying from &packet_buffer[2]. A malformed ClientKeyExchange can advertise a valid-sized identity but provide fewer bytes. Return NX_SECURE_TLS_INCORRECT_MESSAGE_LENGTH before the copy.

@tkEmLogic tkEmLogic May 15, 2026

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Fixed, now returns NX_SECURE_TLS_INCORRECT_MESSAGE_LENGTH if message_length < 2 + tls_credentials -> nx_secure_tls_remote_psk_id_size

if (tls_credentials -> nx_secure_tls_remote_psk_id_size > NX_SECURE_TLS_MAX_PSK_ID_SIZE)
{
return NX_SIZE_ERROR;
}
NX_SECURE_MEMCPY(tls_credentials -> nx_secure_tls_remote_psk_id, &packet_buffer[2], tls_credentials -> nx_secure_tls_remote_psk_id_size);

status = _nx_secure_generate_premaster_secret(ciphersuite, protocol_version, tls_key_material, tls_credentials,
NX_SECURE_TLS_SESSION_TYPE_SERVER, received_remote_credentials,
public_cipher_metadata, public_cipher_metadata_size, tls_ecc_curves);
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